Light-emitting diode (LEDs) can emit light energy in the presence of energy difference resulted from movement of electrons between the n-type semiconductor and the p-type semiconductor. With this mechanism, the LEDs can generate cool light in contrary to incandescent bulbs. Besides, the LEDs are durable and compact, and have long lifespan and low energy-consumption. Accordingly, the LEDs become promising candidates in the market to be the next-generation lighting products in place of the conventional lighting sources, and are already applied to various fields such as traffic lights, backlight modules, street lights, and medical equipment.
As shown in FIG. 1, a light-emitting diode element 100, which can be adapted to an alternative current power source, includes a submount 10, a light-emitting diode array chip 12 on the submount 10, and at least one bonding pad 14 electrically connected to the light-emitting diode array chip 12. The light-emitting diode array chip 12 includes a substrate 120 and several light-emitting diode units 122 on the substrate 120.
To replace a conventional lighting device, the light-emitting diode element 100 must work on a high voltage condition of 100V˜240V, which may bring about a high temperature issue after long time operation. Under the high voltage and high temperature conditions, an electronmigration effect, which is a result of movement of metal ions caused by a mixed effect of the temperature and the electron wind, can be easily found in an electronic device. Generally, the electronmigration of metal ions occurs easily at high temperature. In the light-emitting diode element, the metal ions may diffuse from the electrode to the active region by the effect of the electric current at high temperature. For example, the electronmigration may occur easily in the electrode material such as indium tin oxide (ITO) and silver. Moreover, the element may fail due to voids caused by the electronmigration in solder or tiny metal connection.
As described above, the reliability of the light-emitting diode element for alternative current usage can be seriously deteriorated at high temperature and high voltage environment.